1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly, to a method and an apparatus of driving a plasma display panel.
2. Description of the Background Art
Generally, a plasma display panel (hereinafter abbreviated PDP) displays an image including characters and graphics in a manner of exciting a fluorescent substance by a 147 nm UV-ray emitted from a mixed gas discharge of (He+Xe), (Ne+Xe), or (He+Ne+Xe). PDP displays provide excellent image quality with a slim size and wide-screen due to recent technology developments. Specifically, a 3-electrode AC surface discharge type PDP lowers the voltage necessary for an electric discharge using wall charges accumulated on a surface and protects its electrodes from sputtering that occurs on the electric discharge, thereby enabling low voltage drive and long endurance.
FIG. 1 is a perspective diagram of a discharge cell of a 3-electrode AC surface discharge type PDP according to a related art. Referring to FIG. 1, a discharge cell of a 3-electrode AC surface discharge type PDP consists of a scan electrode 30Y and sustain electrode 30Z formed on an upper substrate 10 and an address electrode 20X formed on a lower substrate 18.
Each of the scan and sustain electrodes 30Y and 30Z has a line width smaller than that of a transparent electrode 12Y or 12Z and includes a metal bus electrode 13Y or 13Z. The transparent electrodes 12Y and 12Z are generally formed of indium tin oxide (ITO) on the upper substrate 10. The metal bus electrodes 13Y and 13Z are generally formed of metal such as Cr or the like on the transparent electrodes 12Y and 12Z to reduce the voltage drops caused by the high resistance of the transparent electrodes 12Y and 12Z, respectively. An upper dielectric layer 14 and protecting layer 16 are stacked over the upper substrate 10 including the scan and sustain electrodes 30Y and 30Z. Wall charges generated from plasma discharge are accumulated on the upper dielectric layer 14. The protecting layer 16 protects the upper dielectric layer 14 against sputtering caused by plasma discharge and increases discharge efficiency of secondary electrons. And, the protecting layer 16 is generally formed of MgO.
The address electrode 20X is formed in a direction crossing with that of the scan or sustain electrode 30Y or 30Z. A lower dielectric layer 22 and barrier rib 24 are formed on the lower substrate 8 having the address electrode 20X formed thereon. A fluorescent layer 26 is formed on surfaces of the lower dielectric layer 22 and the barrier rib 24. The barrier rib 24 is formed parallel to the address electrode 20X to physically partition each discharge cell and prevents UV and visible rays generated from electric discharge from leaking to neighbor discharge cells. The fluorescent layer 26 is excited by the UV-ray generated from plasma discharge to emit light including one of red, green, and blue visible rays. A mixed inert gas such as He+Xe, Ne+Xe, He+Xe+Ne, and the like for electric discharge is injected in a discharge space of the discharge cell provided between the barrier ribs 24 and the upper and lower substrates 10 and 18.
In the above-configured 3-electrode AC surface discharge type PDP, one frame is divided into several sub-fields differing in luminous times to implement gray levels of an image. Each of the sub-fields is also divided into a reset period for arousing electric discharge evenly, an address period for selecting a discharge cell, and a sustain period for implementing gray levels according to a discharging number.
For instance, in case of displaying an image with 256 gray levels, a frame period (16.67 ms) corresponding to 1/60 second is divided into eight sub-fields SF1 To SF8. In addition, each of the eight sub-fields SF1 to SF8 is divided into a reset period, an address period, and a sustain period. The reset and address periods of the respective sub-fields are equal to each other, whereas the sustain periods and their discharge numbers of the respective sub-fields increase at a ratio of 2n (n=0, 1, 2, 3, 4, 5, 6, 7), respectively. As the sustain period varies according to the corresponding sub-field, the image gray levels can be implemented.
Substantially, the sub-fields of the frame are selected to implement the gray levels in a manner of Table 1.
TABLE 1SF1SF2SF3SF4SF5SF6SF7SF8Y1Y2Y3Y8Y16Y32Y64Y128 0XXXXXXXX 1◯XXXXXXX 2X◯XXXXXX 15◯◯◯◯XXXX 16XXXX◯XXX 17◯XXX◯XXX... 31◯◯◯◯◯XXX 32XXXXX◯XX 33◯XXXX◯XX... 63◯◯◯◯◯◯XX 64XXXXXX◯X...127◯◯◯◯◯◯◯X128XXXXXXX◯...255◯◯◯◯◯◯◯◯
In Table 1, ‘SFx’ means an xth sub-field, ‘Yz’ indicates a brightness weight set to a decimal number for the corresponding sub-field, ‘602’ indicates a turned-on state of the corresponding sub-field, and ‘X’ indicates a turned-off state of the corresponding sub-field.
The sub-fields, as shown in Table 1, bring about sustain discharges to correspond to the brightness weights allocated to them, respectively, thereby representing gray levels corresponding to the brightness weights, respectively.
Yet, the related art PDP brings about a problem that Contour Noise takes place by the discord between a light integration direction and a visual characteristic recognizable by human eyes between the gray levels 15-16, 31-32, 63-64, or 127-128 where a luminous pattern considerably varies. For instance, in case that the luminous pattern varies between the gray levels 128 and 127, a luminosity difference between the two frames becomes a value of ‘1’. Yet, if the gray value of ‘127’ is displayed as shown in Table 1, the first to seventh sub-fields SF1 to SF7 become luminous. And, if the gray value of ‘128’ is displayed as shown in Table 1, the eights sub-field SF8 becomes luminous. Namely, when the luminous pattern is changed from ‘128’ to ‘127’, a luminous pattern timing difference between the two frames becomes big to bring about a great movement of a luminous point, whereby Contour Noise occurs.
Meanwhile, in order to eliminate Contour Noise occurring in PDP, a method of displaying a gray level (16, 32, 64, 128), of which luminous pattern considerably changes, on the average has been proposed in the related art. In other words, gray levels of ‘A (e.g., 31)’ and ‘B (e.g., 33)’ are displayed in two neighbor discharge cells, as shown in FIG. 3, to represent a gray level of ‘C. (e.g., 32) on the average. Thus, if the gray level having a greatly changeable pattern is displayed on the average using the gray levels displayed in the neighbor discharge cells, it is advantageous in reducing Contour Noise.
However, as mentioned in the above description, if the gray level having a greatly changeable pattern is displayed on the average, flickering mal-discharge and/or mis-discharge or the like occurs at low temperature of 15˜(−)50° C. or high temperature of 50˜100° C.
Specifically, the gray levels of ‘A’ and ‘B’ are displayed in the discharge cells adjacent to each other, as shown in FIG. 3, to minimize Contour Noise. In doing so, a discharge timing of the gray level of ‘A’ is mostly different from that of the gray level of ‘B’. In other words, one discharge occurs in the first to fifth sub-fields SF1 To SF5 to display the gray level of ‘A (31)’. And, the other discharge occurs in the first to sixth sub-fields SF1 To SF6 to display the gray level of ‘B (32)’. In displaying the gray levels of ‘A’ and ‘B’, the discharges simultaneously occur in the first sub-field SF1 only but fail to occur simultaneously in the rest sub-fields. If the discharges of the neighbor discharge cells occur in the different timings, respectively, i.e., if priming charged particles are produced in the different timings, a specific discharge cell fails to be supplied with the produced priming charged particles when the discharge of the discharge cell adjacent to the specific one takes place. Hence, the flickering mal-discharge and/or discharge failure and the like are brought about at the low and/or high temperature.
In this case, a loss amount of wall charges produced during an initialization period increases as the motion of particles becomes active at the high temperature. Hence, mis-discharge and the like take place when the gray level, of which luminous pattern is greatly changed, is displayed on the average. And, since the particle motion slows down at the low temperature so that erase discharge and the like may fail to occur normally, it is difficult to produce the wall charges corresponding to a demanded amount during the initialization period. Hence, the flickering mal-discharge and the like take place in displaying the gray level having the considerably changeable luminous pattern on the average.
Meanwhile, in another related art, a method of raising brightness with a drive voltage higher than that of a low-density Xe panel by setting a component of Xe among discharge gas sealed within PDP to at least 5% of the discharge gas is proposed. Namely, a high-density Xe panel enables to display an image of high brightness by raising the Xe component of the discharge gas. Yet, since the drive voltage of the high-density Xe panel is set higher than that of the low-density Xe panel, it becomes more probable that the mis-discharge or discharge failure of the high-density Xe panel may occur at the low or high temperature in displaying the gray level having the greatly changeable luminous pattern on the average.